Smoke detector utilizing broadband light

ABSTRACT

In accordance with certain embodiments, a smoke detector utilizes broadband light with a plurality of wavelengths to determine the presence of smoke.

RELATED APPLICATION

This application claims the benefit of and priority to U.S. ProvisionalPatent Application No. 61/639,935, filed Apr. 29, 2012, the entiredisclosure of which is hereby incorporated herein by reference.

FIELD OF THE INVENTION

In various embodiments, the present invention generally relates to smokedetectors and smoke/gas detectors and, in particular, to such detectorshaving external sampling volumes.

BACKGROUND

The “lag time” of a smoke detector is commonly defined as the length oftime from when a threshold smoke density is reached outside the detectorto when the smoke detector responds. In the event of a fire, the lagtime takes away from the Available Safe Egress Time (ASET), the timeavailable for occupants to safely evacuate a building before the firerenders evacuation impossible. Thus, reducing the lag time in a smokedetector is critically important, because it can make the differencebetween life and death.

For ionization and photoelectric smoke detectors, the lag time can besubstantial because both types require the use of an internal sensingchamber to physically isolate the smoke-detecting element from theambient environment. The sensing chamber is typically enclosed by abaffle that restricts the flow of smoke into the chamber, therebydelaying the buildup of smoke compared to the smoke level outside thedetector. Ionization and photoelectric smoke detectors can be combinedwith detectors sensitive to other products of a fire, such as carbonmonoxide (CO) and heat, to lower the threshold smoke density at whichthe smoke detector responds. However, this approach does not remove therestriction on the flow of smoke into the sensing chamber, andsignificant time for smoke detector response is still needed.

Another shortcoming of ionization and photoelectric smoke detectors isthat, in models equipped with a test feature, the testing mechanismtests the electrical circuitry only and not the operation of thesmoke-detecting element. Specifically, activating the test mechanismdoes not introduce any smoke or smoke analog into the sensing chamber totest the response of the smoke detector. Thus, there is no assuranceduring a smoke detector test that the smoke-detecting element hassensitivity to the presence of smoke.

Accordingly, there is a need for detectors for smoke and/or gas, andrelated detection techniques, which decrease lag time and enable testingof the smoke-detecting element.

SUMMARY

In accordance with various embodiments of the present invention, a smokedetector uses a proximity sensor to detect the presence of smoke outsidethe detector. The smoke detector may also utilize an ambient-lightsensor to detect the presence of light emitted by a fire. Additionalembodiments of the invention feature combination smoke/gas detectorsthat use both a proximity sensor to detect the presence of smoke outsidethe detector and a gas sensor to detect the presence of gaseous firebyproducts such as carbon monoxide (CO) or carbon dioxide (CO₂).

The proximity sensor generally operates by emitting a beam of light anddetecting any reflected signal from an object located within a specifiedrange. A light detector is embedded in the proximity sensor along withcontrol circuitry and signal processing circuitry. The light emitter mayalso be embedded, or it may be discrete but externally driven by theproximity sensor. An ambient-light sensor may also be embedded withinthe proximity sensor. Alternative embodiments of the invention use adiscrete light emitter and light detector in place of the proximitysensor without altering the functionality of the smoke detector. Asutilized herein, a “light detector” is a discrete or embedded electroniccomponent that registers the presence of and/or measures a property oflight (e.g., luminance, wavelength, etc.) when it is illuminated by thelight.

In accordance with various embodiments of the invention, the proximitysensor is disposed inside the housing of the smoke detector beneath asingle opening. The opening may or may not be covered by a window thatis at least partially transparent to the emitted light. Some of theemitted beam from the proximity sensor is reflected back by the housingand window, generating a background signal. The remainder of the emittedbeam passes through the opening to the environment outside the smokedetector. The region outside the smoke detector but within the specifiedrange of the proximity sensor (or other discrete components describedherein) is defined herein as the “external sampling volume.” If smoke oran obstruction enters the external sampling volume, the signal generatedby the proximity sensor will increase. In the case of smoke, theincrease in signal arises from scattering of the emitted beam by thesmoke particles. In the case of an obstruction, the increase in signalcomes from the reflection of the emitted beam by the obstruction.

An evaluation circuit may continuously analyze the signal to determinewhether an obstruction, smoke, or system fault is present. Sincereflection by an obstruction typically produces a distinctly strongersignal than scattering by smoke particles, an obstruction threshold isset higher than the maximum possible signal generated by smokescattering. If the signal exceeds the obstruction threshold for apre-determined amount of time, an obstruction alarm may be activated.This pre-determined delay typically eliminates unwanted alarms fromfleeting events such as an insect passing through the external samplingvolume.

The smoke threshold is generally set lower than the obstructionthreshold but higher than the background signal, and the smoke thresholdmay correspond to the signal generated for a given smoke density outsidethe detector. If additional sensors are incorporated in the smokedetector, such as a gas or ambient-light sensor, the smoke threshold maybe decreased with increasing signal from these sensors, as the signalfrom the additional sensor provides faster activation and greaterdiscrimination from nuisance sources (i.e., false alarms). An advantageof embodiments of the present invention is that the proximity sensordirectly measures the smoke density outside the smoke detector, whichsubstantially reduces the lag time compared to a conventional ionizationor photoelectric smoke detector.

Embodiments of the invention typically feature a system fault thresholdset at a level lower than the background signal. The background signalis typically dependent on the operation of the light detector and lightemitter, and if it falls below the system fault threshold, it indicatesa fault in the proximity sensor or control circuitry, and a system faultalarm may be activated. This technique enables continuous, automatictesting of the smoke-detecting element. The operation of the smokedetector may also be manually tested by inserting an object, such as ahand or broom handle, into the external sampling volume to activate theobstruction alarm after a pre-determined delay has elapsed. Likewise,inserting an object into the external sampling volume while an alarm isactivated may temporarily silence the alarm.

In an aspect, embodiments of the invention feature a smoke detector thatincludes or consists essentially of a housing, a light source disposedwithin the housing, one or more light detectors disposed within thehousing, and an evaluation circuit. The light source is configured todirect light outside of the housing, and the directed light includes aplurality of different wavelengths. The one or more light detectors areconfigured to detect light from the light source that is reflected backinto the housing. The evaluation circuit determines the presence ofsmoke particles outside the housing based at least in part on adifference between a luminance of a first wavelength of the detectedlight and a luminance of a second wavelength of the detected light,wherein the second wavelength is different from the first wavelength.

Embodiments of the invention may include one or more of the following inany of a variety of different combinations. The light source may includeor consist essentially of a plurality of different light emitters eachemitting light of at least one of the different wavelengths. Each lightemitter may include or consist essentially of a light-emitting diode ora laser. The light source may include or consist essentially of abroadband light source emitting light of the plurality of differentwavelengths, e.g., a white light-emitting diode. The light source may beconfigured to emit an interior portion of light within the housingsubstantially without emission therefrom. At least one light detectormay be configured to detect light from the interior light portion withinthe housing. The presence of smoke particles outside the housing may bedetermined based in part on a luminance of light detected from theinterior light portion. The housing may define an opening for emittingtherethrough the directed light and admitting therethrough lightreflected from the directed light. The light source may be configured toemit an interior portion of light within the housing substantiallywithout emission therefrom, and light from the interior light portionmay be reflected by a portion of the housing proximate the opening. Thehousing may include a window, substantially transparent to a wavelengthof light emitted by the light source, for emitting therethrough thedirected light and admitting therethrough light reflected from thedirected light. The light source may be configured to emit an interiorportion of light within the housing substantially without emissiontherefrom, and light from the interior light portion may be reflected bythe window. The light source and the one or more light detectors may beportions of a single electronic component, e.g., a proximity sensor. Thelight source and the one or more light detectors may not be portions ofa single electronic component.

A gas sensor may be disposed at least partially within or on thehousing. The presence of smoke particles outside the housing may bedetermined based in part on (i) a gas concentration sensed by the gassensor and/or (ii) a temporal evolution of the gas concentration sensedby the gas sensor. The gas sensor may be configured to sense carbonmonoxide and/or carbon dioxide. The light source may emit visible and/orinfrared light. The evaluation circuit may be configured to determinethe presence of a non-smoke physical obstruction outside the housingbased at least in part on a luminance and/or a rate of change ofluminance of the detected light. The light source may be configured toemit an interior portion of light within the housing substantiallywithout emission therefrom, at least one light detector may beconfigured to detect light from the interior light portion within thehousing, and the evaluation circuit may be configured to determine thepresence of a non-smoke physical obstruction outside the housing basedin part on a luminance of light detected from the interior lightportion. A manual test button may be disposed on the housing andelectrically connected to the evaluation circuit. After actuation of themanual test button, the evaluation circuit may perform a test sequencebased at least in part on the luminance of the detected light. The lightsource may be configured to emit an interior portion of light within thehousing substantially without emission therefrom, at least one lightdetector may be configured to detect light from the interior lightportion within the housing, and the test sequence may be based in parton a luminance of the detected interior light portion. The one or morelight detectors may include or consist essentially of a plurality oflight detectors each sensitive to light of a different wavelength. Anambient-light sensor, for sensing the ambient light level outside thehousing, may be disposed at least partially within or on the housing.The presence of smoke particles outside the housing may be determinedbased in part on (i) an ambient light level sensed by the ambient-lightsensor and/or (ii) a temporal evolution of the ambient light levelsensed by the ambient-light sensor. The ambient-light sensor may sensevisible and/or infrared light.

In another aspect, embodiments of the invention feature a method ofsmoke detection. Light of a plurality of different wavelengths isemitted outside a housing. Light from the emitted light reflected backinto the housing is detected. The presence of smoke particles outsidethe housing is determined based at least in part on a difference betweena luminance of a first wavelength of the detected light and a luminanceof a second wavelength of the detected light, where the secondwavelength is different from the first wavelength.

Embodiments of the invention may include one or more of the following inany of a variety of different combinations. An interior portion of lightmay be emitted within the housing substantially without emissiontherefrom, and light from the interior light portion may be detectedwithin the housing. The presence of smoke particles outside the housingmay be determined based in part on the detected light from the interiorlight portion. A maintenance alarm may be activated if a luminance ofthe detected light from the interior light portion falls below amaintenance threshold. A test sequence, based at least in part on theluminance of the detected light reflected back into the housing and theluminance of the detected interior light portion, may be performed. Theemitted light may be emitted through an opening in the housing andreflected back into the housing through the opening. An interior portionof light may be emitted to reflect within the housing substantiallywithout emission therefrom, light from the interior light portion withinthe housing may be detected after reflection thereof, and the presenceof smoke particles outside the housing may be determined based in parton the detected light from the interior light portion. The emitted lightmay be emitted through a window in the housing and reflected back intothe housing through the window. The window may be substantiallytransparent to the plurality of different wavelengths. An interiorportion of light may be emitted to reflect from the window within thehousing substantially without emission therefrom, light from theinterior light portion within the housing may be detected afterreflection thereof, and the presence of smoke particles outside thehousing may be determined based in part on the detected light from theinterior light portion.

The detected light may be detected by a plurality of light detectorseach sensitive to a different wavelength of light. A gas concentrationoutside the housing may be sensed. The presence of smoke particlesoutside the housing may be determined based in part on the sensed gasconcentration. The gas concentration may be a concentration of carbonmonoxide and/or carbon dioxide. A single electronic component, e.g., aproximity sensor, may emit light and detect the reflected light. Theambient light level outside the housing may be sensed. The presence ofsmoke particles outside the housing may be determined based in part on(i) the ambient light level and/or (ii) a temporal evolution of theambient light level.

In an aspect, embodiments of the invention feature a smoke detectorincluding or consisting essentially of a housing, a light sourcedisposed within the housing, one or more light detectors disposed withinthe housing, and an evaluation circuit. The light source is configuredto (i) emit a first light portion outside of the housing and (ii) emit asecond light portion within the housing substantially without emissiontherefrom. The one or more light detectors are configured to receivelight from the first light portion reflected back into the housing andlight from the second light portion within the housing. The evaluationcircuit determines the presence of smoke particles outside the housingbased at least in part on (i) the light received by the one or morelight detectors from the first light portion and (ii) the light receivedby the one or more light detectors from the second light portion.

Embodiments of the invention may include one or more of the following inany of a variety of different combinations. The presence of smokeparticles outside the housing may be determined based on (i) a luminanceand/or a rate of change of luminance of light received from the firstlight portion, and (ii) a luminance of light received from the secondlight portion. The housing may define an opening for emittingtherethrough the first light portion and admitting therethrough lightfrom the first light portion reflected back into the housing. Light fromthe second light portion may be reflected by a portion of the housingproximate the opening. The housing may include a window, substantiallytransparent to a wavelength of light emitted by the light source, foremitting therethrough the first light portion and admitting therethroughlight from the first light portion reflected back into the housing.Light from the second light portion may be reflected by the window. Thelight source and the one or more light detectors may be portions of asingle electronic component, e.g., a proximity sensor. The light sourceand the one or more light detectors may not be portions of a singleelectronic component (and may thus be separate electronic componentsthat are independently operable). A gas sensor may be disposed at leastpartially within or on the housing. The presence of smoke particlesoutside the housing may be determined based in part on (i) a gasconcentration sensed by the gas sensor and/or (ii) a temporal evolutionof the gas concentration sensed by the gas sensor. The gas sensor may beconfigured to sense carbon monoxide and/or carbon dioxide. The lightsource may emit visible and/or infrared light.

The evaluation circuit may be configured to determine the presence of anon-smoke physical obstruction outside the housing based on (i) aluminance and/or a rate of change of light received from the first lightportion, and (ii) a luminance of light received from the second lightportion. A manual test button may be disposed on the housing andelectrically connected to the evaluation circuit. After actuation of themanual test button, the evaluation circuit may perform a test sequencebased at least in part on the luminance of the received first lightportion and the luminance of the received second light portion. Thelight source may include or consist essentially of a broadband lightsource emitting light over a range of wavelengths, e.g., a whitelight-emitting diode. The one or more light detectors may include orconsist essentially of a plurality of light detectors each sensitive tolight over only a portion of the range of wavelengths. The light sourcemay include or consist essentially of a plurality of light emitters eachemitting light of a different wavelength, and the first light portionmay include or consist essentially of light at each of the differentwavelengths. The presence of smoke particles outside the housing may bedetermined based in part on a difference between luminance of lightreceived from the first light portion of a first wavelength andluminance of light received from the first light portion of a secondwavelength different from the first wavelength. The one or more lightdetectors may include or consist essentially of a plurality of lightdetectors each sensitive to light of a different wavelength. Anambient-light sensor for sensing the ambient light level outside thehousing may be disposed at least partially within or on the housing. Thepresence of smoke particles outside the housing may be determined basedin part on (i) an ambient light level sensed by the ambient-light sensorand/or (ii) a temporal evolution of the ambient light level sensed bythe ambient-light sensor. The ambient-light sensor may sense visibleand/or infrared light.

In another aspect, embodiments of the invention feature a method ofsmoke detection. A first light portion is emitted outside a housing. Asecond light portion is emitted within the housing substantially withoutemission therefrom. Light from the first light portion reflected backinto the housing and light from the second light portion within thehousing are detected. The presence of smoke particles outside thehousing is determined based at least in part on (i) the detected lightfrom the first light portion and (ii) the detected light from the secondlight portion

Embodiments of the invention may include one or more of the following inany of a variety of different combinations. The presence of smokeparticles outside the housing may be determined based on (i) a luminanceand/or a rate of change of luminance of detected light from the firstlight portion, and (ii) a luminance of detected light from the secondlight portion. The first light portion may be emitted through an openingin the housing and the light from the first portion reflected back intothe housing may be admitted through the opening. Light from the secondlight portion may reflect within the housing prior to being detected.The first light portion may be emitted through a window in the housingand the light from the first portion reflected back into the housing maybe admitted through the window. The window may be substantiallytransparent to a wavelength of the first light portion. Light from thesecond light portion may reflect from the window prior to beingdetected. Light reflected from the first light portion and light fromthe second light portion may be detected by the same light detector. Amaintenance alarm may be activated if a luminance of the detected lightfrom the second light portion falls below a maintenance threshold.

A gas concentration outside the housing, e.g., a concentration of carbonmonoxide and/or carbon dioxide, may be sensed. The presence of smokeparticles outside the housing may be determined based in part on thesensed gas concentration. A single electronic component, e.g., aproximity sensor, may emit the first light portion and receive lightreflected from the first light portion. A test sequence may be performedbased at least in part on the luminance of the detected first lightportion and the luminance of the detected second light portion. Thefirst light portion may include or consist essentially of light of aplurality of different wavelengths. The presence of smoke particlesoutside the housing may be determined based in part on a differencebetween luminance of light detected from the first light portion of afirst wavelength and luminance of light detected from the first lightportion of a second wavelength different from the first wavelength. Anambient light level outside the housing may be sensed. The presence ofsmoke particles outside the housing may be determined based in part on(i) the ambient light level and/or (ii) a temporal evolution of theambient light level.

In yet another aspect, embodiments of the invention feature a method ofsmoke detection. A first light portion is emitted from within a housingat a first time. Light from the first light portion reflected back intothe housing is sensed. The sensed light reflected from the first lightportion is compared to a first threshold and to a second thresholdlarger than the first threshold. At a second time later than the firsttime, only if the luminance of the sensed light reflected from the firstlight portion is larger than the first threshold and less than thesecond threshold, (a) light continues to be emitted outside of thehousing to reflect back into the housing, (b) later-emitted lightreflected back into the housing is sensed, and a rate of change of aluminance of only the sensed later-emitted light is compared to a thirdthreshold. A smoke alarm is activated if the rate of change exceeds thethird threshold.

Embodiments of the invention may include one or more of the following inany of a variety of different combinations. If the rate of change of theluminance of the sensed later-emitted light is smaller than the thirdthreshold, steps (a)-(c) may be repeated until the rate of change issmaller than a nuisance threshold smaller than the third threshold. Anobstruction alarm may be activated if the luminance of the sensed lightfrom the first light portion is larger than the second threshold. Asecond light portion may be emitted within the housing without emissiontherefrom. Light from the second light portion may be sensed within thehousing. The first threshold and/or the second threshold may be based atleast in part on a luminance of sensed light from the second lightportion. Light reflected from the first light portion and light from thesecond light portion may be sensed by the same light detector. Amaintenance alarm may be activated if a luminance of the sensed lightfrom the second light portion falls below a maintenance threshold. A gasconcentration outside the housing, e.g., a concentration of carbonmonoxide and/or carbon dioxide, may be sensed. The third threshold maybe changed based on the sensed gas concentration, for example, the thirdthreshold may be decreased as the sensed gas concentration increases.Only if the rate of change of the luminance of sensed later-emittedlight is smaller than the third threshold, (i) a gas alarm time may bedetermined based on the sensed gas concentration and an elapsed time. Agas alarm may be activated if the gas alarm time is larger than a gasalarm time threshold. A single electronic component, e.g., a proximitysensor, may emit the first light portion and sense light reflected fromthe first light portion. A test sequence may be activated. During thetest sequence, the smoke alarm may be activated if the luminance ofsensed light from the first light portion is larger than the firstthreshold or larger than the second threshold. The test sequence may beexited sequence if, during a time period after activation of the testsequence, the luminance of sensed light from the first light portionremains below the first threshold.

In an aspect, embodiments of the invention feature a smoke detector thatincludes or consists essentially of a housing, a light source disposedwithin the housing, one or more light detectors disposed within thehousing, an ambient-light sensor disposed at least partially within oron the housing, and an evaluation circuit. The light source isconfigured to direct light outside of the housing. The one or more lightdetectors are configured to detect light from the light source that isreflected back into the housing. The ambient-light sensor senses theambient light level outside of the housing. The evaluation circuitdetermines the presence of smoke particles outside the housing based atleast in part on the detected light and (i) the sensed ambient lightlevel and/or (ii) a temporal evolution of the sensed ambient lightlevel.

Embodiments of the invention may include one or more of the following inany of a variety of different combinations. The presence of smokeparticles outside the housing may be determined based in part on aluminance and/or a rate of change of luminance the detected light. Theambient-light sensor may sense visible and/or infrared light. The lightsource may be configured to emit an interior portion of light within thehousing substantially without emission therefrom. At least one lightdetector may be configured to detect light from the interior lightportion within the housing. The presence of smoke particles outside thehousing may be determined based in part on a luminance of light detectedfrom the interior light portion. The housing may define an opening foremitting therethrough the directed light and admitting therethroughlight reflected from the directed light. The light source may beconfigured to emit an interior portion of light within the housingsubstantially without emission therefrom, and light from the interiorlight portion may be reflected by a portion of the housing proximate theopening. The housing may include a window, substantially transparent toa wavelength of light emitted by the light source, for emittingtherethrough the directed light and admitting therethrough lightreflected from the directed light. The light source may be configured toemit an interior portion of light within the housing substantiallywithout emission therefrom, and light from the interior light portionmay be reflected by the window. The light source and the one or morelight detectors may be portions of a single electronic component, e.g.,a proximity sensor. The light source and the one or more light detectorsmay not be portions of a single electronic component. A gas sensor maybe disposed at least partially within or on the housing. The presence ofsmoke particles outside the housing may be determined based in part on(i) a gas concentration sensed by the gas sensor and/or (ii) a temporalevolution of the gas concentration sensed by the gas sensor. The gassensor may be configured to sense carbon monoxide and/or carbon dioxide.The light source may emits visible and/or infrared light.

The evaluation circuit may be configured to determine the presence of anon-smoke physical obstruction outside the housing based at least inpart on a luminance and/or a rate of change of luminance of the detectedlight. The light source may be configured to emit an interior portion oflight within the housing substantially without emission therefrom, atleast one light detector may be configured to detect light from theinterior light portion within the housing, and the evaluation circuitmay be configured to determine the presence of a non-smoke physicalobstruction outside the housing based in part on a luminance of lightdetected from the interior light portion. A manual test button may bedisposed on the housing and electrically connected to the evaluationcircuit. After actuation of the manual test button, the evaluationcircuit may perform a test sequence based at least in part on theluminance of the detected light. The light source may be configured toemit an interior portion of light within the housing substantiallywithout emission therefrom, at least one light detector may beconfigured to detect light from the interior light portion within thehousing, and the test sequence may be based in part on a luminance ofthe detected interior light portion. The light source may include orconsist essentially of a broadband light source emitting light over arange of wavelengths, e.g., a white light-emitting diode. The one ormore light detectors may include or consist essentially of a pluralityof light detectors each sensitive to light over only a portion of therange of wavelengths. The light source may include or consistessentially of a plurality of light emitters each emitting light of adifferent wavelength, and the directed light may include each of thedifferent wavelengths. The presence of smoke particles outside thehousing may be determined based in part on a difference between aluminance of a first wavelength of the detected light and a luminance ofa second wavelength of the detected light, where the second wavelengthis different from the first wavelength. The one or more light detectorsmay include or consist essentially of a plurality of light detectorseach sensitive to light of a different wavelength.

In another aspect, embodiments of the invention feature a method ofsmoke detection. A first light portion is emitted outside a housing.Light from the emitted light reflected back into the housing isdetected. The ambient light level outside of the housing is sensed. Thepresence of smoke particles outside the housing is determined based atleast in part on the detected light and (i) the sensed ambient lightlevel and/or (ii) a temporal evolution of the sensed ambient lightlevel.

Embodiments of the invention may include one or more of the following inany of a variety of different combinations. The presence of smokeparticles outside the housing may be determined based in part on aluminance and/or a rate of change of luminance of the detected light. Aninterior portion of light may be emitted within the housingsubstantially without emission therefrom. Light from the interior lightportion may be detected within the housing. The presence of smokeparticles outside the housing may be determined based in part on thedetected light from the interior light portion. A maintenance alarm maybe activated if a luminance of the detected light from the interiorlight portion falls below a maintenance threshold. A test sequence,based at least in part on the luminance of the detected light reflectedback into the housing and the luminance of the detected interior lightportion, may be performed. The first light portion may be emittedthrough an opening in the housing and reflected back into the housingthrough the opening. An interior portion of light may be emitted toreflect within the housing substantially without emission therefrom,light from the interior light portion may be detected within the housingafter reflection thereof, and the presence of smoke particles outsidethe housing may be determined based in part on the detected light fromthe interior light portion. The emitted light may be emitted through awindow in the housing and reflected back into the housing through thewindow. The window may be substantially transparent to a wavelength ofthe emitted light. An interior portion of light may be emitted toreflect from the window within the housing substantially withoutemission therefrom, light from the interior light portion may bedetected within the housing after reflection thereof, and the presenceof smoke particles outside the housing may be determined based in parton the detected light from the interior light portion.

The detected light may be detected by a plurality of light detectorseach sensitive to a different wavelength of light. A gas concentrationoutside the housing, e.g., a concentration of carbon monoxide and/orcarbon dioxide, may be sensed. The presence of smoke particles outsidethe housing may be determined based in part on the sensed gasconcentration. A single electronic component, e.g., a proximity sensor,may emit light and detect the reflected light. The emitted light mayinclude a plurality of different wavelengths. The presence of smokeparticles outside the housing may be determined based in part on adifference between a luminance of a first wavelength of the detectedlight and a luminance of a second wavelength of the detected light,wherein the second wavelength is different from the first wavelength.

These and other objects, along with advantages and features of theinvention, will become more apparent through reference to the followingdescription, the accompanying drawings, and the claims. Furthermore, itis to be understood that the features of the various embodimentsdescribed herein are not mutually exclusive and can exist in variouscombinations and permutations. Reference throughout this specificationto “one example,” “an example,” “one embodiment,” or “an embodiment”means that a particular feature, structure, or characteristic describedin connection with the example is included in at least one example ofthe present technology. Thus, the occurrences of the phrases “in oneexample,” “in an example,” “one embodiment,” or “an embodiment” invarious places throughout this specification are not necessarily allreferring to the same example. Furthermore, the particular features,structures, routines, steps, or characteristics may be combined in anysuitable manner in one or more examples of the technology. The term“light” broadly connotes any wavelength or wavelength band in theelectromagnetic spectrum, including, without limitation, visible light,ultraviolet radiation, and infrared radiation. Similarly, photometricterms such as “luminance,” “luminous flux,” and “luminous intensity”extend to and include their radiometric equivalents, such as “radiance,”“radiant flux,” and “radiant intensity.” As used herein, a “portion oflight” means an intensity or directional fraction of light that may ormay not be discrete from other portions of the same light. As usedherein, the term “substantially” means ±10%, and in some embodiments,±5%. The term “consists essentially of” means excluding other materialsthat contribute to function, unless otherwise defined herein.Nonetheless, such other materials may be present, collectively orindividually, in trace amounts.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like reference characters generally refer to the sameparts throughout the different views. Also, the drawings are notnecessarily to scale, emphasis instead generally being placed uponillustrating the principles of the invention. In the followingdescription, various embodiments of the present invention are describedwith reference to the following drawings, in which:

FIG. 1A is a cross-sectional diagram of a smoke detector with a discretelight emitter and light detector in accordance with various embodimentsof the invention;

FIG. 1B is a cross-sectional diagram of a smoke detector with aproximity sensor featuring an embedded light detector and an externallydriven light emitter in accordance with various embodiments of theinvention;

FIG. 1C is a cross-sectional diagram of a smoke detector with aproximity sensor featuring an embedded light detector and light emitterin accordance with various embodiments of the invention;

FIGS. 2A-2D illustrate various signal-generation techniques utilized indetectors in accordance with various embodiments of the invention;

FIG. 2E is a block diagram of an evaluation circuit in accordance withvarious embodiments of the invention;

FIG. 3 is a cross-sectional diagram of a combination smoke/gas detectorwith a discrete light emitter and light detector in accordance withvarious embodiments of the invention;

FIG. 4A is a cross-sectional diagram of a smoke detector with a discretelight emitter, light detector, and ambient-light sensor in accordancewith various embodiments of the invention;

FIG. 4B is a cross-sectional diagram of a smoke detector with aproximity sensor featuring an embedded light emitter, light detector,and ambient-light sensor in accordance with various embodiments of theinvention;

FIG. 4C illustrates signal generation from smoke located in a samplingvolume and light emitted by a fire in accordance with variousembodiments of the invention;

FIG. 5A is a cross-sectional diagram of a smoke detector with a discretelight detector and multiple light emitters emitting at differentwavelengths in accordance with various embodiments of the invention;

FIG. 5B is a cross-sectional diagram of a smoke detector with multiplelight detectors responsive to different wavelengths and a discretebroadband light emitter in accordance with various embodiments of theinvention;

FIG. 5C illustrates signal generation from smoke located in a samplingvolume using multiple light emitters in accordance with variousembodiments of the invention;

FIG. 6 is a flow chart depicting the standby mode of operation of acombination smoke/gas detector in accordance with various embodiments ofthe invention;

FIG. 7 is a flow chart depicting the testing mode of operation of acombination smoke/gas detector in accordance with various embodiments ofthe invention;

FIG. 8 is a flow chart depicting the gas warning mode of operation of acombination smoke/gas detector in accordance with various embodiments ofthe invention; and

FIG. 9 is a flow chart depicting the smoke warning mode of operation ofa combination smoke/gas detector in accordance with various embodimentsof the invention.

DETAILED DESCRIPTION

FIG. 1A depicts a smoke detector in accordance with various embodimentsof the invention. As shown, the smoke detector includes a discrete lightdetector 100 and light emitter 102 that are mounted onto a circuit board110 (or otherwise mounted within a surrounding housing 120). Anevaluation circuit 104 may also be mounted on the circuit board 110. Allof these components are disposed inside a smoke-detector housing 120,which includes or consists essentially of one or more rigid materials(e.g., metal, plastic, etc.). In various embodiments of the invention,the housing 120 has a single opening 130 that is situated over the lightdetector 100 and light emitter 102. (As shown in FIG. 1A, the opening130 is “over” the light detector 100 and light emitter 102 in the sensethat it is disposed opposite the circuit board 110 on which thesecomponents are mounted; in embodiments in which the smoke detector ismounted, e.g., on a ceiling, the opening 130 would be disposed “under”or “beneath” the light detector 100 and light emitter 102 as pictured.)The light detector 100 includes or consists essentially of one or moredevices that register the presence of and/or measure a property thelight illuminating the device(s). For example, the light detector 100may produce charge (i.e., an electronic signal) when exposed to light.Exemplary light detectors 100 include photodiodes, photodetectors,photoconductors, and/or photocapacitors. The light emitter 102 mayinclude or consist essentially of, e.g., one or more light-emittingdiodes (LEDs) or lasers.

FIGS. 1B and 1C depict additional embodiments of the present invention.In FIG. 1B, the light detector 100 is embedded in a proximity sensor 106that may control the operation of the light emitter 102, while the lightemitter 102 remains a discrete component. An exemplary proximity sensor106 in this embodiment is the Silicon Laboratories Si1141Proximity/Ambient Light Sensor. In FIG. 1C, both the light detector 100and light emitter 102 are embedded in the proximity sensor 106. Anexemplary proximity sensor 106 in this embodiment is the VishayIntertechnology VCNL4000 Fully Integrated Proximity and Ambient LightSensor. As depicted in the example of FIG. 1C, the light detector 100and light emitter 102 may be portions of a single electronic component,i.e., disposed within a single discrete package and/or on the sameprinted circuit board or other means of electrical interconnection.

Electronic signals are generated when light emitted by the light emitter102 is collected (or “sensed” or “detected”) by the light detector 100.As shown in FIG. 2A, a signal may be generated when an emitted beam 200from the light emitter 102 partially reflects off the housing 120. Atleast some of the reflected beam 202 is collected by the light detector100. Furthermore, as shown in FIG. 2B, at least a portion of a beam 204reflected (due to, e.g., Fresnel reflection) from a window 210 disposedwithin (and at least partially closing) the opening 130 may be collectedby the light detector 100, generating a signal. The window 210 mayinclude or consist essentially of, e.g., plastic and/or glass, and isgenerally at least partially transparent to the emitted beam 200.

As might be expected, signals may also be generated due to scatteringfrom smoke particles. FIG. 2C depicts smoke particles 220 present in theexternal sampling volume due to, e.g., a nearby fire. The emitted beam200 from the light emitter 102 passes through the opening in the housing120 and is scattered by the smoke particles 220 to form a scattered beam206. At least some of the scattered beam 206 passes back through theopening in housing 120 and is collected by the light detector 100.

Signals may also be generated by the smoke detector in response toobstructions in the external sampling volume. FIG. 2D depicts anobstruction 230 present in the external sampling volume. The obstruction230 may be any object other than smoke particles, such as but notlimited to a person, furniture, or cleaning instrument. As shown, theemitted beam 200 from the light emitter 102 passes through the opening130 in the housing 120 and is reflected from the obstruction 230,generating a reflected beam 208. At least some of the reflected beam 208passes back through the opening 130 in housing 120 and is collected bythe light detector 100.

The opening 130 in the housing 120 may be situated such that most of thelight emitted by the light emitter 102 passes through the opening 130 tothe external sampling volume, but a portion is reflected off the housing120 or window 210 and does not pass through to the outside environment.In alternative embodiments, the opening 130 in the housing 120 issituated such that substantially all of the light emitted by the lightemitter 102 passes through the opening 130 to the external samplingvolume.

The emission wavelength of the light emitter 102 may be any wavelength,including ultraviolet, visible, or infrared, but the infrared ispreferred because it is invisible to the human eye and, when emitted inlow-energy pulses, is eye-safe (i.e., does not result in damage to thehuman eye). In various embodiments of the invention, the light emittedby the light emitter 102 is pulsed to reduce power consumption and totemporally distinguish the signal from any ambient light sources.

At least a portion of the signal collected by the light detector 100 istypically transmitted to the evaluation circuit 104, which analyzes thesignal to determine whether there is an obstruction alarm, smoke alarm,or system fault alarm. FIG. 2E schematically depicts various componentsof the evaluation circuit 104, which may include (but not be limited to)a memory 240, a receiver 250, a signal analyzer 260, a transformer 270,a controller 280, and/or a timer 290. The memory 240 may storepre-determined values (e.g., thresholds) utilized in sensing and/orcontrol operations, and/or may store various signal values during and/orafter they are sensed and/or transformed (e.g., smoothed). At least aportion of memory 240 may be volatile, and at least a portion of memory240 may be non-volatile. The receiver 250 may receive signals from othercomponents of the smoke detector (e.g., light detectors and othersensors) and route the signals to other portions of the evaluationcircuit 104. The signal analyzer 260 may compare received (and/ortransformed) signals to various pre-determined threshold levels and/orto previously received (and/or transformed) signals to determine ifsmoke, a non-smoke obstruction, and/or a fault condition is present. Thetransformer 270 may transform received signals to, e.g., reduce oreliminate noise and/or compensate for drift. For example, thetransformer 270 may implement smoothing (e.g., exponential smoothingand/or moving-average smoothing), filtering (e.g., high-pass, low-pass,and/or band-pass filtering), regression, and/or other numericaltransformation techniques. The controller 280 may control othercomponents of the smoke detector; for example, the controller 280 maycontrol speakers that emit audible alarms and/or light sources inresponse to a sensed alarm condition or as part of a test sequence. Thetimer 290 may measure time elapsed during or since various sensedconditions and/or may be utilized to measure pre-determined delaysutilized in various sensing or testing sequences.

The evaluation circuit 104 (and/or any or all of its components) may bea general-purpose microprocessor, but depending on implementation mayalternatively be a microcontroller, peripheral integrated circuitelement, a customer-specific integrated circuit (CSIC), anapplication-specific integrated circuit (ASIC), a logic circuit, adigital signal processor, a programmable logic device such as afield-programmable gate array (FPGA), a programmable logic device (PLD),a programmable logic array (PLA), an RFID processor, smart chip, or anyother device or arrangement of devices that is capable of implementingthe steps of the processes of embodiments of the invention. In apreferred embodiment, the evaluation circuit 104 is a microcontroller.The evaluation circuit 104 may be monolithically integrated with, andthus a portion of the same integrated-circuit chip as, light detector100 and/or proximity sensor 106, or evaluation circuit 104 may bedisposed on a chip separate and discrete from the chip containing lightdetector 100 and/or proximity sensor 106 (and interconnected thereto bywired or wireless means). Moreover, at least some of the functions ofevaluation circuit 104 may be implemented in software and/or as mixedhardware-software modules. Software programs implementing thefunctionality herein described may be written in any of a number of highlevel languages such as FORTRAN, PASCAL, JAVA, C, C++, C#, BASIC,various scripting languages, and/or HTML. Additionally, the software maybe implemented in an assembly language directed to a microprocessorresident in evaluation circuit 104. The software may be embodied on anarticle of manufacture including, but not limited to, a floppy disk, ajump drive, a hard disk, an optical disk, a magnetic tape, a PROM, anEPROM, EEPROM, field-programmable gate array, CDROM, or DVDROM.Embodiments using hardware-software modules may be implemented using,for example, one or more FPGA, CPLD, or ASIC processors.

To minimize the effects of noise and drift in the detected signal, theevaluation circuit 104 may apply smoothing to the signal. In a preferredembodiment, the smoothing is an exponential smoothing. Specifically, fora current sensor reading x, the smoothed signal S is assigned thefollowing value:

S:=αx+(1−α)S,

where α is the smoothing factor. As implied by the use of the assignmentoperator (‘:=’) in the above expression, the smoothed signal S may beupdated without the use of another variable. The smoothing factor a isin the range of 0<α<1.

In various embodiments of the present invention, slowly varying andquickly varying signals may be distinguished by calculating two smoothedsignals and taking the difference. The first smoothed signal has alarger smoothing factor a, typically in the range of 0.01<α<1. It maytrack signals that change over the course of seconds to minutes withoutsignificant lag. The second smoothed signal has a smaller smoothingfactor a, typically in the range of 0.0001<α<0.01. It may only tracksignals that change over the course of tens of minutes to hours withoutsignificant lag.

Of the four above-described ways to generate a signal, reflection fromthe housing 120 and reflection from the window 210 contribute to abackground signal that is typically constant or, if any drift ispresent, relatively slowly varying. Both the first and second smoothedsignals may track these signals without significant lag. Thedifferential signal in this case will typically be approximately zero.In contrast, scattering by smoke particles 220 and reflection from anobstruction 230 result in signals that are relatively quickly varying.The first smoothed signal may track these signals without significantlag but the second generally will not. If the smoke scattering or objectreflection is strong enough, the differential signal in this case mayexceed an alarm threshold.

If the second smoothed signal is ever larger than the first smoothedsignal, which may occur if there is a decrease in the detected signal,then the second smoothed signal is assigned the value of the firstsmoothed signal. This ensures the differential signal will always bepositive when there is an increase in the detected signal, so that anypotential alarm condition will not be delayed or undetected.

Furthermore, smoke scattering and object reflection may be distinguishedby evaluating the signal, or the differential signal detailed above,hereafter collectively referred to as the signal. This may beaccomplished by establishing two thresholds, an obstruction thresholdand a smoke threshold. A solid object has a much larger cross-sectionalarea than smoke particles; therefore, the object will generally producea distinctly stronger signal than the smoke particles, even for veryhigh smoke obscurations (or densities) of greater than 40%/ft. Thus, theobstruction threshold is preferably set higher than the signal generatedwhen the smoke obscuration is approximately 40%/ft. If the signalexceeds the obstruction threshold for a pre-determined amount of time,an obstruction alarm (i.e., an audible tone or visible light) may beactivated. The pre-determined delay eliminates unwanted (or “false”)alarms from fleeting events such as an insect passing through theexternal sampling volume.

The smoke threshold is typically set lower than the obstructionthreshold but higher than the background signal. The smoke threshold maycorrespond to the signal generated when the smoke obscuration exceedsapproximately 2%/ft but not greater than approximately 10%/ft in theexternal sampling volume. If the signal exceeds the smoke threshold fora pre-determined amount of time, a smoke alarm (i.e., an audible tone orvisible light) may be activated. The smoke alarm may be different fromthe obstruction alarm in tone, duration, volume, intensity, and/orfrequency.

In various embodiments of the present invention, automatic systemtesting is performed by comparing the detected signal to a system faultthreshold, which is set lower than the background signal typicallyreceived by the light detector 100 and/or proximity sensor 106. Thebackground-signal level may be dependent on the operation and/orphysical structure of the light detector 100 and/or light emitter 102.If the signal falls below the system fault threshold, it generallyindicates a fault in at least one of these components, the proximitysensor 106, or evaluation circuit 104, and a system fault alarm (i.e.,an audible tone or visible light) is activated. The system fault alarmmay be different from the obstruction alarm and/or the smoke alarm intone, duration, volume, intensity, and/or frequency.

Manual system testing of the smoke detector may be performed byinserting an object, such as a hand or broom handle, into the externalsampling volume for a pre-determined amount of time (e.g., a minimumduration of 2-20 seconds) to intentionally increase the signal andactivate either the obstruction alarm or smoke alarm. If an alarm isalready activated, an object may be inserted into the external samplingvolume for a pre-determined amount of time to temporarily or permanently(at least for the currently sensed condition and/or until the smokedetector is reset) silence the alarm.

To provide more rapid activation for smoke detection and greaterdiscrimination from nuisance sources, additional sensors sensitive tofire byproducts other than smoke (e.g., one or more gases and/or light)may be disposed within the smoke detector to operate in tandem with theproximity sensor 106 or light detector 100. The signals collected by theadditional sensors are typically also transmitted to the evaluationcircuit 104 by wired or wireless means. The evaluation circuit 104 mayapply smoothing to these additional signals.

FIG. 3 depicts a combination gas/smoke detector that includes a gassensor 300, e.g., within the housing 120 and/or mounted on the circuitboard 110. The gas sensor 300 may detect, for example, CO or CO₂. If thesignal from the gas sensor 300 increases, the evaluation circuit 104 maydecrease the smoke threshold. That is, if any additional gas such as COor CO₂ is present above background levels, the smoke threshold may beadjusted to the signal generated when the smoke obscuration exceeds,e.g., approximately 1%/ft.

In embodiments of the invention in which the gas sensor 300 is a COsensor, the combination smoke/gas detector may also serve as astandalone CO detector. If a pre-determined CO concentration level hasbeen exceeded for a given amount of time, a CO alarm (i.e., an audibletone or visible light) may be activated. For example, in UL 2034, theStandard for Safety of Single and Multiple Station Carbon MonoxideAlarms (the entire disclosure of which is incorporated by referenceherein), the CO alarm must activate in no less than 60 minutes and nogreater than 240 minutes when the CO concentration is 70±5 ppm, no lessthan 10 minutes and no greater than 50 minutes when the CO concentrationis 150±5 ppm, and no less 4 minutes and no greater than 15 minutes whenthe CO concentration is 400±10 ppm. The CO alarm may be different fromthe obstruction alarm, the system fault alarm, and/or the smoke alarm intone, duration, volume, intensity, and/or frequency.

Smoke detectors in accordance with various embodiments of the presentinvention may also incorporate ambient-light sensors. As shown in FIG.4A, an exemplary smoke detector features an ambient-light sensor 400,e.g., within the housing 120 and/or mounted onto the circuit board 110.As shown in FIG. 4B, the ambient-light sensor 400 may be embedded withinthe proximity sensor 106 along with light detector 100 and/or lightemitter 102.

As illustrated in FIG. 4C, an ambient signal is generated when anemitted beam 412 from a fire 410 passes through the opening 130 in thehousing 120 and is collected by the ambient-light sensor 400. If thesignal from the ambient-light sensor 400 increases, the evaluationcircuit 104 may decrease the smoke threshold. That is, if any additionallight is present above background levels, the smoke threshold may beadjusted to the signal generated when, e.g., the smoke obscurationexceeds ˜1%/ft. The ambient-light sensor 400 is generally sensitive tovisible light, but it may also be sensitive to ultraviolet and/orinfrared light. There are many other sources than fire that may increasethe signal detected by the ambient-light sensor 400, such as room lightsturning on or sunlight intensifying on a partly cloudy day. However,none of these alone will typically activate the smoke alarm because anobject must still be present in the external sampling volume.

When the ambient signal is calculated using the differential signaltechnique described above, a first smoothed signal and second smoothedsignal are calculated. If the second smoothed signal is ever higher thanthe first smoothed signal, which may occur if there is a decrease in thedetected signal, then the second smoothed signal is assigned the valueof the first smoothed signal. This ensures the differential signal willalways be positive when there is an increase in the detected signal, sothat any potential alarm condition will not be delayed or undetected.Furthermore, if there is a long-term increase in the detected signal,such as the room lights turning on for an extended period, thedifferential signal, initially large, will eventually decay to zero asthe second smoothed signal finally tracks the detected signal. When thisoccurs, the smoke threshold is adjusted back to its original value whenno additional light is detected.

Greater discrimination from nuisance sources may also be achieved bygenerating multiple signals each using distinct wavelengths of light.Airborne particles other than smoke, such as dust, powders, or watervapor, scatter the various wavelengths of light throughout the nearultraviolet, visible, and near infrared (e.g., wavelengths ofapproximately 300-1000 nm) generally equally because these particleshave a diameter on the order of several microns. However, smokeparticles, which typically have a diameter of less than one micron,typically scatter the shorter wavelengths of light much more stronglythan the longer wavelengths. By using multiple light emitters, at leastone with a shorter emission wavelength, such as blue, violet, orultraviolet (e.g., wavelengths of approximately 300-480 nm), and atleast one with a longer emission wavelength, such as red or infrared(e.g., wavelengths of approximately 630-1000 nm), the relative signalsmay be compared to determine whether the airborne particles within theexternal sampling volume are smoke particles or not. As known to thoseof skill in the art, light emitters such as LEDs and lasers that emit atparticular wavelengths may be produced by, e.g., selection and/oradjustment of the band gap and/or lasing cavity size of asemiconductor-based light emitter.

FIG. 5A depicts an embodiment of the present invention in which thesmoke detector incorporates multiple light emitters each emitting at adifferent wavelength. As shown, the light detector 100, a red lightemitter 500, and a blue light emitter 502 are mounted onto the circuitboard 110 and/or within the housing 120. In various embodiments, the redlight emitter 500 emits red and/or infrared light, and the blue lightemitter 502 emits blue, violet, and/or ultraviolet light. Generally, theblue light emitter 502 emits light of a shorter wavelength than lightemitted by red light emitter 500. The opening 130 in housing 120 may besituated over the light detector 100, red light emitter 500, and bluelight emitter 502. In other embodiments of the present invention, aseparate light detector may be utilized for each light emitter in thesmoke detector.

In various embodiments of the present invention, a broad spectrum oflight may be emitted from the smoke detector, and multiple differentlight detectors, each with a sensitivity to a different wavelength orrange of wavelengths, may be utilized. As shown in FIG. 5B, a firstlight detector 510, a second light detector 512, and a broadband lightemitter 514 may be disposed within the housing 120 and/or mounted ontothe circuit board 110. The first light detector 510 and second lightdetector 512 have different sensitivities to different wavelengths. Forexample, the first light detector 510 may be more sensitive to redand/or infrared light, and the second light detector 512 may be moresensitive to blue, violet, and/or ultraviolet light. In another example,the first light detector 510 may be sensitive to both visible andinfrared light, and the second light detector 512 may be sensitive toonly visible light. The broadband emitter 514 typically emits light overa wide range of wavelengths, and may include or consist essentially ofone or more white LEDs (i.e., LEDs that emit white light or mixed lightthat closely approximates white light). Multiple different lightemitters with different emission wavelengths, as depicted in FIG. 5A,may also be used in conjunction with the multiple light detectors 510,512. As known to those of skill in the art, light detectors such asphotodetectors that are sensitive to light of particular wavelengths maybe produced by, e.g., selection and/or adjustment of the band gap of asemiconductor-based light detector.

As shown in FIG. 5C, at least two signals may be generated when airborneparticles 530 are present in the external sampling volume. A red emittedbeam 520 from red light emitter 500 may pass through the opening 130 inthe housing 120 and be scattered by the airborne particles 530,generating a red scattered beam 522. At least some of the red scatteredbeam 522 may pass back through the opening 130 in housing 120 and becollected by the light detector 100, producing a “red signal.” A blueemitted beam 524 from blue light emitter 502 may also pass through theopening 130 in housing 120 and be scattered by the airborne particles530. At least some of the blue scattered beam 526 may pass back throughthe opening 130 in housing 120 and be collected by the light detector100, generating a “blue signal.” The light emitted by the red lightemitter 500 and blue light emitter 502 may be separately pulsed totemporally distinguish the signals from any ambient light sources andfrom each other. For example, only one of the light emitters 500, 502may be emitting light at any particular time.

The signals collected by the light detector 100 may be transmitted tothe evaluation circuit 104, which analyzes the signals to determinewhether the airborne particles 530 are smoke particles or not. Theevaluation circuit 104 may apply smoothing to these signals, asdescribed above. In an embodiment of the invention, if the blue signalexceeds a smoke threshold and the ratio between the increase in the bluesignal to the increase in the red signal exceeds a pre-determinedthreshold (e.g., approximately 2:1), then it is determined the airborneparticles 530 are smoke particles, and the smoke alarm is activated.Otherwise, if the ratio between the increase in the blue signal to theincrease in the red signal does not exceed the pre-determined threshold,then it is determined the airborne particles 530 are not smokeparticles, and the smoke alarm is not activated.

As mentioned above, in various embodiments the evaluation circuit 104analyzes the temporal pattern of detected signal(s) to determine whetherthere is a smoke alarm condition, gas (e.g., CO and/or CO₂) alarmcondition, physical obstruction, and/or system fault. Another exemplarytechnique of determining which condition is present, if any, isillustrated in FIGS. 6-9.

An exemplary standby sequence 600 is illustrated in FIG. 6. The standbysequence 600 may be the normal sequence followed by a smoke/gas detectorwhen both the smoke and gas detector signals have not exceeded anythreshold values. In the following discussion, CO is utilized as anexemplary detected gas; however, this example is not meant to belimiting, and embodiments of the present invention encompass detectionand/or alarming for one or more gases (e.g., CO₂) instead of or inaddition to CO.

In a process step 602, the smoke detector signal S and CO detectorsignal C, if available, are measured. Under standby operation, when noobject is present in the external sampling volume, the only signalcontribution to S is typically from light emitted by the lightemitter(s) reflecting off the housing or window. If no CO is present, Cis approximately zero.

In a decision step 604, if S is less than a specified fault threshold,then a system fault 614 is activated. Because S is typically dependenton the operation of the light emitter(s), light detector(s), and controlcircuitry, if it falls below the fault threshold, then one or more ofthese components is typically not operating properly. This exemplarytechnique thus includes continuous, automatic testing of thesmoke-detecting element. This decision step 604 is generally onlyapplicable if the housing or window reflects back a measurable portionof light emitted by the light emitter(s).

In a decision step 606, if a test button on the smoke detector, ifavailable, is depressed, then the test sequence 700 is executed. Thetest sequence 700 enables manual testing of the smoke-detecting elementand is described in more detail below.

In a decision step 608, if S is greater than a specified obstructionthreshold, then an obstruction alarm 616 is activated. When smoke ispresent in the external sampling volume, even with a very highobscuration density, the amount of scattered light from the smoke istypically still less than the amount of reflected light from a physicalobstruction in the external sampling volume. This is particularly truebecause smoke typically would not build up to a high obscuration densitywithin one measurement cycle of standby sequence 600, whereas a physicalobstruction may be inserted into the external sampling volume within onemeasurement cycle, leading to a large increase in S between cycles. Theobstruction threshold is set at a level that cannot reasonably bereached by the buildup of smoke within one measurement cycle.

In a decision step 610, if C is greater than a specified CO alertthreshold, then a CO warning sequence 800 is executed. Standards for COalarm activation usually specify a minimum CO concentration that must bereached before alarm activation may occur. The CO alert threshold maycorrespond to this minimum CO concentration, typically 30±3 ppm.

In a decision step 612, if S is greater than a specified smoke alertthreshold, then a smoke warning sequence 900 is executed. The smokealert threshold is typically less than the obstruction threshold butgreater than the fault threshold. As with almost any electrical signal,the smoke detector signal S will typically contain noise, which may becharacterized as a random signal added to the “true” signal. Asdescribed above, a smoothing technique, such as exponential smoothing ora simple or weighted moving average, may be applied to reduce the noisein S. The smoke alert threshold is set at a level that cannot reasonablybe reached through the addition of noise.

In decision step 612, if S is less than the smoke alert threshold, thestandby sequence 600 is repeated, starting with process step 602. Sinceeach measurement typically relies upon light emission from the lightemitter(s) and processing by the evaluation circuit, a short delay (forexample of approximately 0.1-10 seconds) may be inserted betweensubsequent measurements to reduce power consumption of the smokedetector. Such reduction in power consumption may be important when thesmoke detector is powered by a battery to increase battery lifetime.

The test sequence 700 is illustrated in FIG. 7. As explained above, thissequence is executed when the test button on the smoke detector isdepressed (and/or when an object is inserted into the external samplingvolume) and enables manual testing of the smoke detector. Brief visualor audio feedback, such as the illumination of a visible LED (or otherlight source) or chirp of a buzzer, may be given immediately after thetest button is depressed to alert the user that the smoke detector hasbegun the test sequence and is anticipating an object to be insertedinto the sampling volume.

In a process step 702, the smoke detector signal S is measured. In adecision step 704, if S is greater than the specified smoke alertthreshold, then a smoke alarm 910 is activated. This will occur if anobject, such as a hand or broom handle, is intentionally inserted intothe sampling volume. In this case, the object insertion is intentionalbecause it occurs shortly after the test button is depressed. Thistechnique may provide assurance that all critical components of thesmoke detector are operational.

In a decision step 706, if a specified duration of, for example,approximately 2-20 seconds has elapsed before S exceeds the smoke alertthreshold, then the standby sequence 600 is again executed. Because thetest sequence 700 is simplified in scope compared to the standbysequence 600, a time limit ensures that the smoke detector does not stayin the test sequence 700 for an extended duration so that safety is notcompromised.

In decision step 706, if the specified duration has not elapsed, thetest sequence 700 is repeated, starting with process step 702. Sinceeach measurement relies upon light emission from the light emitter(s)and processing by the evaluation circuit, a short delay (for example ofapproximately 0.1-10 seconds) may be inserted between subsequentmeasurements to reduce power consumption of the smoke detector.

The CO warning sequence 800 is illustrated in FIG. 8. As explainedabove, this sequence is executed when the CO detector signal C isgreater than the specified CO alert threshold. Its purpose is to monitorthe temporal evolution of the CO concentration and determine if a COalarm condition is present, or if smoke is simultaneously detected, toexecute the smoke warning sequence.

In a process step 802, the elapsed time t is set to zero. Standards forCO alarm activation are usually based on reaching a specified percentageof carboxyhemoglobin (COHb) in the blood, which is dependent on both theCO concentration and exposure time. The CO warning sequence 800 thuspreferably monitors both C and t.

In a process step 804, the smoke detector S and CO detector signal C aremeasured. In a decision step 806, if C is less than the CO alertthreshold, the CO warning sequence 800 is exited and the standbysequence 600 is again executed. As explained above, the requirement forCO alarm activation is that C must exceed the CO alert threshold. Ifthis condition were met again when back in the standby sequence 600, theCO warning sequence 800 will be executed again.

In a decision step 808, if S is greater than the smoke alert threshold,then the smoke warning sequence 900 is executed. In this case, bothsmoke and CO have been detected, which is typically indicative of a fireinstead of a CO leak. The smoke warning sequence 900 is thus typicallygiven precedence over the CO warning sequence 800.

In a process step 810, a CO alarm time is calculated based on C. Variousembodiments of the invention utilize one or more standards for CO alarmactivation. For example, in UL 2034, the Standard for Safety of Singleand Multiple Station Carbon Monoxide Alarms (the entire disclosure ofwhich is incorporated by reference herein), the CO alarm must activatein no less than 60 minutes and no greater than 240 minutes when the COconcentration is 70±5 ppm, no less than 10 minutes and no greater than50 minutes when the CO concentration is 150±5 ppm, and no less 4 minutesand no greater than 15 minutes when the CO concentration is 400±10 ppm.

In a decision step 812, if t is greater than the CO alarm time, then theCO alarm 814 is activated. Alternately, if the estimated percentage ofCOHb is greater than an alarm threshold, then the CO alarm 814 isactivated.

In decision step 812, if t is less than the CO alarm time, then the COwarning sequence 800 is repeated, starting with process step 804. Sinceeach measurement relies upon light emission from the light emitter(s)and processing by the evaluation circuit, a short delay (for example ofapproximately 0.1-10 seconds) may be inserted between subsequentmeasurements to reduce power consumption of the detector.

The smoke warning sequence 900 is illustrated in FIG. 9. As explainedabove, this sequence is executed when the smoke detector signal S isgreater than the specified smoke alert threshold. Its purpose, invarious embodiments, is to monitor the temporal evolution of the smokeconcentration and CO concentration, if available, and determine whethera fire or a nuisance source is present.

When the smoke warning sequence 900 is executed, either an object hasbeen detected in the sampling volume, or there is drift in the proximitysensor or control circuitry, or the ambient conditions have suddenlychanged, such as the room lights turning on. To determine whether thesource is smoke or a nuisance source, embodiments of the inventiondetermine whether S is still increasing at a sufficient rate, which maybe accomplished by monitoring the trend (slope) S′ after the smoke alertthreshold has been exceeded. There are many methods to calculate S′; oneexemplary method is double exponential smoothing, in which case aninitial value close to zero may be assigned to S′. An advantage ofdouble exponential smoothing is that it may smooth out the noise in Sand S′.

Smoke typically builds up in an approximately monotonically increasingmanner, so that S likewise increases monotonically and S′ has somepositive value after just a few measurement cycles, especially whendouble exponential smoothing is used. By contrast, the signal from anuisance source—a physical obstruction, signal drift, or abruptlychanging ambient conditions—will generally either remain approximatelyconstant or decrease, so that S′ has a value that is approximately zeroor negative.

In a process step 902, the smoke detector S and CO detector signal C aremeasured, and the trend S′ is calculated. As noted above, thecalculation of S′ typically begins only after the smoke warning sequence900 is executed.

In a process step 904, a trend alarm threshold is calculated based on C.The trend alarm threshold decreases with increasing C, which enablesmore rapid detection when both smoke and CO are present. It alsoprovides greater discrimination from nuisance sources that do notproduce CO. If no CO detector is present, then the trend alarm thresholdtypically has a fixed value. If an ambient-light sensor is present, thenthe trend alarm threshold may also be decreased as the amount of ambientlight increases.

In a decision step 906, if S′ is greater than the trend alarm threshold,then the smoke alarm 910 is activated, as there is smoke present. In adecision step 908, if S′ is less than a specified nuisance threshold,then the smoke warning sequence 900 is exited and the standby sequence600 is again executed, as the source of the signal is a nuisance source.

In decision step 908, if S′ is greater than the specified nuisancethreshold, then the smoke warning sequence 900 is repeated, startingwith process step 902. The smoke warning sequence 900 is repeated untileither S′ is greater than the trend alarm threshold or less than thenuisance threshold. Since each measurement relies upon light emissionfrom the light emitter(s) and processing by the evaluation circuit, ashort delay (for example of approximately 0.1-10 seconds) may beinserted between subsequent measurements to reduce power consumption ofthe smoke detector.

The terms and expressions employed herein are used as terms andexpressions of description and not of limitation, and there is nointention, in the use of such terms and expressions, of excluding anyequivalents of the features shown and described or portions thereof. Inaddition, having described certain embodiments of the invention, it willbe apparent to those of ordinary skill in the art that other embodimentsincorporating the concepts disclosed herein may be used withoutdeparting from the spirit and scope of the invention. Accordingly, thedescribed embodiments are to be considered in all respects as onlyillustrative and not restrictive.

What is claimed is:
 1. A smoke detector comprising: a housing; disposedwithin the housing, a light source configured to direct light outside ofthe housing, the directed light comprising a plurality of differentwavelengths; disposed within the housing, one or more light detectorsconfigured to detect light from the light source that is reflected backinto the housing; and an evaluation circuit for determining the presenceof smoke particles outside the housing based at least in part on adifference between a luminance of a first wavelength of the detectedlight and a luminance of a second wavelength of the detected light,wherein the second wavelength is different from the first wavelength. 2.The smoke detector of claim 1, wherein the light source comprises aplurality of different light emitters each emitting light of at leastone of the different wavelengths.
 3. The smoke detector of claim 2,wherein each light emitter comprises a light-emitting diode or a laser.4. The smoke detector of claim 1, wherein the light source comprises abroadband light source emitting light of the plurality of differentwavelengths.
 5. The smoke detector of claim 4, wherein the broadbandlight source comprises a white light-emitting diode.
 6. The smokedetector of claim 1, wherein (i) the light source is configured to emitan interior portion of light within the housing substantially withoutemission therefrom, (ii) at least one said light detector is configuredto detect light from the interior light portion within the housing, and(iii) the presence of smoke particles outside the housing is determinedbased in part on a luminance of light detected from the interior lightportion.
 7. The smoke detector of claim 1, wherein the housing definesan opening for emitting therethrough the directed light and admittingtherethrough light reflected from the directed light.
 8. The smokedetector of claim 7, wherein (i) the light source is configured to emitan interior portion of light within the housing substantially withoutemission therefrom, and (ii) light from the interior light portion isreflected by a portion of the housing proximate the opening.
 9. Thesmoke detector of claim 1, wherein the housing comprises a window,substantially transparent to a wavelength of light emitted by the lightsource, for emitting therethrough the directed light and admittingtherethrough light reflected from the directed light.
 10. The smokedetector of claim 9, wherein (i) the light source is configured to emitan interior portion of light within the housing substantially withoutemission therefrom, and (ii) light from the interior light portion isreflected by the window.
 11. The smoke detector of claim 1, wherein thelight source and the one or more light detectors are portions of asingle electronic component.
 12. The smoke detector of claim 11, whereinthe electronic component comprises a proximity sensor.
 13. The smokedetector of claim 1, wherein the light source and the one or more lightdetectors are not portions of a single electronic component.
 14. Thesmoke detector of claim 1, further comprising a gas sensor disposed atleast partially within or on the housing.
 15. The smoke detector ofclaim 14, wherein the presence of smoke particles outside the housing isdetermined based in part on at least one of (i) a gas concentrationsensed by the gas sensor or (ii) a temporal evolution of the gasconcentration sensed by the gas sensor.
 16. The smoke detector of claim14, wherein the gas sensor is configured to sense at least one of carbonmonoxide or carbon dioxide.
 17. The smoke detector of claim 1, whereinthe light source emits at least one of visible or infrared light. 18.The smoke detector of claim 1, wherein the evaluation circuit isconfigured to determine the presence of a non-smoke physical obstructionoutside the housing based at least in part on at least one of aluminance or a rate of change of luminance of the detected light. 19.The smoke detector of claim 18, wherein (i) the light source isconfigured to emit an interior portion of light within the housingsubstantially without emission therefrom, (ii) at least one said lightdetector is configured to detect light from the interior light portionwithin the housing, and (iii) the evaluation circuit is configured todetermine the presence of a non-smoke physical obstruction outside thehousing based in part on a luminance of light detected from the interiorlight portion.
 20. The smoke detector of claim 1, further comprising amanual test button disposed on the housing and electrically connected tothe evaluation circuit, wherein, after actuation of the manual testbutton, the evaluation circuit performs a test sequence based at leastin part on the luminance of the detected light.
 21. The smoke detectorof claim 20, wherein (i) the light source is configured to emit aninterior portion of light within the housing substantially withoutemission therefrom, (ii) at least one said light detector is configuredto detect light from the interior light portion within the housing, and(iii) the test sequence is based in part on a luminance of the detectedinterior light portion.
 22. The smoke detector of claim 1, wherein theone or more light detectors comprise a plurality of light detectors eachsensitive to light of a different wavelength.
 23. The smoke detector ofclaim 1, further comprising an ambient-light sensor, disposed at leastpartially within or on the housing, for sensing an ambient light leveloutside the housing.
 24. The smoke detector of claim 23, wherein thepresence of smoke particles outside the housing is determined based inpart on at least one of (i) an ambient light level sensed by theambient-light sensor or (ii) a temporal evolution of the ambient lightlevel sensed by the ambient-light sensor.
 25. The smoke detector ofclaim 23, wherein the ambient-light sensor senses at least one ofvisible or infrared light.